The inventive concept relates to a semiconductor memory device, and more particularly, to a memory system based on a nonvolatile semiconductor memory and an operation control method thereof.
A semiconductor memory device may be classified into a volatile memory device such as a DRAM, a SRAM, etc. and a nonvolatile memory device such as an EEPROM, a FRAM, a PRAM, a MRAM, a flash memory, etc. A volatile memory device loses its stored data when its power is interrupted while a nonvolatile memory device retains its stored data even when its power is interrupted. A flash memory has advantages of a high programming speed, low power consumption, a high-capacity data storage, etc. Thus, a memory system including a flash memory is being widely used as data storage medium.
A flash memory device stores bit information by injecting charge into a conductive floating gate isolated by an insulating layer. However, because of a capacitive coupling problem that may exist between memory cells or between a memory cell and a select transistor (GSL, SSL), a conductive floating gate structure may be considered as a structure having a physical limit in high density integration. As an alternative to addressing a capacitive coupling issue between conductive floating gates, a charge trap flash (CTF) memory structure using an insulating layer such as Si3N4, Al2O3, HfAlO, HfSiO, etc. as a charge storage layer is being suggested.
A charge trap flash (CTF) memory device may be applied to a three-dimensional flash memory device to overcome a physical limit of high density integration. Because of a structural feature of using an insulating layer as a charge storage layer, in a charge trap flash (CTF) memory device, electrons or holes in a charge storage layer are rearranged or recombined after a program or erase operation and thereby threshold voltages of flash memory cells may be changed.
If threshold voltages of flash memory cells are changed due to a disturbance phenomenon in a read operation, a UECC (uncorrectable error correction code) may occur in the read data.